This invention generally relates to the recovery of carbon dioxide from a feed stream.
Large scale processing systems for recovering carbon dioxide from a feed stream are known in the art. Typically such systems while different in the details of operation are similar in complexity to systems which are used to carry out the cryogenic separation of air into its components and thus employ heat exchangers having relatively complicated structures as do processes required for the rigorous cryogenic separation of air. Such complicated structures are costly and it would be desirable to have a system for producing carbon dioxide which can employ a more advantageous heat exchanger arrangement.
Accordingly it is an object of this invention to provide a system for effectively producing carbon dioxide from a feed stream while employing an improved heat exchanger arrangment from that employed by conventional carbon dioxide recovery systems.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is a method for producing carbon dioxide comprising:
(A) passing carbon dioxide feed fluid through a cooling section of a heat exchanger having a cooling section, a desuperheating section and an evaporating section to produce cooled carbon dioxide feed fluid;
(B) passing cooled carbon dioxide feed fluid into a separation means, such as a column, and producing carbon dioxide product fluid in the separation means;
(C) recovering carbon dioxide product fluid from the lower portion of the separation means as product carbon dioxide; and
(D) passing carbon dioxide product fluid through one of the evaporating section and the desuperheating section of the heat exchanger, and passing refrigerant fluid through one of the evaporating section and the desuperheating section of the heat exchanger.
Another aspect of the invention is apparatus for producing carbon dioxide comprising:
(A) a heat exchanger having a cooling section, a desuperheating section and an evaporating section, and means for passing carbon dioxide feed fluid to the cooling section of the heat exchanger;
(B) a separation means and means for passing carbon dioxide feed fluid from the cooling section of the heat exchanger to the separation means;
(C) means for recovering carbon dioxide product fluid from the lower portion of the separation means;
(D) means for passing carbon dioxide product fluid from the lower portion of the separation means through one of the desuperheating section and evaporating section of the heat exchanger, and means for passing refrigerant fluid through one of the evaporating section and the desuperheating section of the heat exchanger.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluid streams into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the terms xe2x80x9cupper portionxe2x80x9d and xe2x80x9clower portionxe2x80x9d mean those sections of a column respectively above and below the mid point of the column.
As used herein the term xe2x80x9ccolumnxe2x80x9d means a distillation or fractionation column or zone, i.e. a contacting column or zone, wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see the Chemical Engineer""s Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. 
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Distillation is the separation process whereby heating of a liquid mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases can be adiabatic or nonadiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns.
As used herein the term xe2x80x9ccooling sectionxe2x80x9d means a section of a heat exchanger wherein a fluid stream releases heat indirectly to one or more other fluid streams thereby cooling and/or condensing that stream.
As used herein the term xe2x80x9cdesuperheating sectionxe2x80x9d means a section of a heat exchanger wherein a fluid stream is cooled with an accompanying decrease in temperature and the heat exchange is carried out without a phase change, i.e. boiling or condensation.
As used herein the term xe2x80x9cevaporating sectionxe2x80x9d means a section of a heat exchanger wherein a fluid stream absorbs heat and is at least partially vaporized.
As used herein the term xe2x80x9crefrigerant fluidxe2x80x9d means a fluid which absorbs heat and is subsequently compressed and condensed against another fluid.